Coagulation Cascade

Overview

Tests

• PT (extrinsic pathway)
  • tests function of factors
    • I
    • II
    • V
    • VII 
    • X
  • defect in any of these → ↑ PT
  • best test to follow warfarin therapy 
    • normalized as an INR (international normalized ratio)
    • note also increases PTT time
  • also used to measure hepatic function as most of the factor are synthesized in the liver
• PTT (intrinsic pathway)
  • tests function of all factors EXCEPT
    • VII
    • XIII
  • defect in any of these→ ↑ PTT 
    • XII also leads to defect in bradykinin activation
  • best test to follow heparin therapy 
• note also increases PT time

Clinical Importance

• Hemophilia A/B  
• Protein C/S deficiency 
• Factor V Leiden 
• Vitamin K deficiency 
• Antithrombin
  • activated by heparin
  • deficiency